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<body class="article">
<div id="header">
<h1>Git index format</h1>
</div>
<div id="content">
<div class="sect1">
<h2 id="_the_git_index_file_has_the_following_format">The Git index file has the following format</h2>
<div class="sectionbody">
<div class="literalblock">
<div class="content">
<pre><code>All binary numbers are in network byte order. Version 2 is described
here unless stated otherwise.</code></pre>
</div></div>
<div class="ulist"><ul>
<li>
<p>
A 12-byte header consisting of
</p>
<div class="literalblock">
<div class="content">
<pre><code>4-byte signature:
  The signature is { 'D', 'I', 'R', 'C' } (stands for "dircache")</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>4-byte version number:
  The current supported versions are 2, 3 and 4.</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>32-bit number of index entries.</code></pre>
</div></div>
</li>
<li>
<p>
A number of sorted index entries (see below).
</p>
</li>
<li>
<p>
Extensions
</p>
<div class="literalblock">
<div class="content">
<pre><code>Extensions are identified by signature. Optional extensions can
be ignored if Git does not understand them.</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>Git currently supports cached tree and resolve undo extensions.</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>4-byte extension signature. If the first byte is 'A'..'Z' the
extension is optional and can be ignored.</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>32-bit size of the extension</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>Extension data</code></pre>
</div></div>
</li>
<li>
<p>
160-bit SHA-1 over the content of the index file before this
     checksum.
</p>
</li>
</ul></div>
</div>
</div>
<div class="sect1">
<h2 id="_index_entry">Index entry</h2>
<div class="sectionbody">
<div class="literalblock">
<div class="content">
<pre><code>Index entries are sorted in ascending order on the name field,
interpreted as a string of unsigned bytes (i.e. memcmp() order, no
localization, no special casing of directory separator '/'). Entries
with the same name are sorted by their stage field.</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>32-bit ctime seconds, the last time a file's metadata changed
  this is stat(2) data</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>32-bit ctime nanosecond fractions
  this is stat(2) data</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>32-bit mtime seconds, the last time a file's data changed
  this is stat(2) data</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>32-bit mtime nanosecond fractions
  this is stat(2) data</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>32-bit dev
  this is stat(2) data</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>32-bit ino
  this is stat(2) data</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>32-bit mode, split into (high to low bits)</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>4-bit object type
  valid values in binary are 1000 (regular file), 1010 (symbolic link)
  and 1110 (gitlink)</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>3-bit unused</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>9-bit unix permission. Only 0755 and 0644 are valid for regular files.
Symbolic links and gitlinks have value 0 in this field.</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>32-bit uid
  this is stat(2) data</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>32-bit gid
  this is stat(2) data</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>32-bit file size
  This is the on-disk size from stat(2), truncated to 32-bit.</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>160-bit SHA-1 for the represented object</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>A 16-bit 'flags' field split into (high to low bits)</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>1-bit assume-valid flag</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>1-bit extended flag (must be zero in version 2)</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>2-bit stage (during merge)</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>12-bit name length if the length is less than 0xFFF; otherwise 0xFFF
is stored in this field.</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>(Version 3 or later) A 16-bit field, only applicable if the
"extended flag" above is 1, split into (high to low bits).</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>1-bit reserved for future</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>1-bit skip-worktree flag (used by sparse checkout)</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>1-bit intent-to-add flag (used by "git add -N")</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>13-bit unused, must be zero</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>Entry path name (variable length) relative to top level directory
  (without leading slash). '/' is used as path separator. The special
  path components ".", ".." and ".git" (without quotes) are disallowed.
  Trailing slash is also disallowed.</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>The exact encoding is undefined, but the '.' and '/' characters
are encoded in 7-bit ASCII and the encoding cannot contain a NUL
byte (iow, this is a UNIX pathname).</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>(Version 4) In version 4, the entry path name is prefix-compressed
  relative to the path name for the previous entry (the very first
  entry is encoded as if the path name for the previous entry is an
  empty string).  At the beginning of an entry, an integer N in the
  variable width encoding (the same encoding as the offset is encoded
  for OFS_DELTA pack entries; see pack-format.txt) is stored, followed
  by a NUL-terminated string S.  Removing N bytes from the end of the
  path name for the previous entry, and replacing it with the string S
  yields the path name for this entry.</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>1-8 nul bytes as necessary to pad the entry to a multiple of eight bytes
while keeping the name NUL-terminated.</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>(Version 4) In version 4, the padding after the pathname does not
exist.</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>Interpretation of index entries in split index mode is completely
different. See below for details.</code></pre>
</div></div>
</div>
</div>
<div class="sect1">
<h2 id="_extensions">Extensions</h2>
<div class="sectionbody">
<div class="sect2">
<h3 id="_cached_tree">Cached tree</h3>
<div class="literalblock">
<div class="content">
<pre><code>Cached tree extension contains pre-computed hashes for trees that can
be derived from the index. It helps speed up tree object generation
from index for a new commit.</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>When a path is updated in index, the path must be invalidated and
removed from tree cache.</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>The signature for this extension is { 'T', 'R', 'E', 'E' }.</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>A series of entries fill the entire extension; each of which
consists of:</code></pre>
</div></div>
<div class="ulist"><ul>
<li>
<p>
NUL-terminated path component (relative to its parent directory);
</p>
</li>
<li>
<p>
ASCII decimal number of entries in the index that is covered by the
    tree this entry represents (entry_count);
</p>
</li>
<li>
<p>
A space (ASCII 32);
</p>
</li>
<li>
<p>
ASCII decimal number that represents the number of subtrees this
    tree has;
</p>
</li>
<li>
<p>
A newline (ASCII 10); and
</p>
</li>
<li>
<p>
160-bit object name for the object that would result from writing
    this span of index as a tree.
</p>
<div class="literalblock">
<div class="content">
<pre><code>An entry can be in an invalidated state and is represented by having
a negative number in the entry_count field. In this case, there is no
object name and the next entry starts immediately after the newline.
When writing an invalid entry, -1 should always be used as entry_count.</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>The entries are written out in the top-down, depth-first order.  The
first entry represents the root level of the repository, followed by the
first subtree---let's call this A---of the root level (with its name
relative to the root level), followed by the first subtree of A (with
its name relative to A), ...</code></pre>
</div></div>
</li>
</ul></div>
</div>
<div class="sect2">
<h3 id="_resolve_undo">Resolve undo</h3>
<div class="literalblock">
<div class="content">
<pre><code>A conflict is represented in the index as a set of higher stage entries.
When a conflict is resolved (e.g. with "git add path"), these higher
stage entries will be removed and a stage-0 entry with proper resolution
is added.</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>When these higher stage entries are removed, they are saved in the
resolve undo extension, so that conflicts can be recreated (e.g. with
"git checkout -m"), in case users want to redo a conflict resolution
from scratch.</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>The signature for this extension is { 'R', 'E', 'U', 'C' }.</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>A series of entries fill the entire extension; each of which
consists of:</code></pre>
</div></div>
<div class="ulist"><ul>
<li>
<p>
NUL-terminated pathname the entry describes (relative to the root of
    the repository, i.e. full pathname);
</p>
</li>
<li>
<p>
Three NUL-terminated ASCII octal numbers, entry mode of entries in
    stage 1 to 3 (a missing stage is represented by "0" in this field);
    and
</p>
</li>
<li>
<p>
At most three 160-bit object names of the entry in stages from 1 to 3
    (nothing is written for a missing stage).
</p>
</li>
</ul></div>
</div>
<div class="sect2">
<h3 id="_split_index">Split index</h3>
<div class="literalblock">
<div class="content">
<pre><code>In split index mode, the majority of index entries could be stored
in a separate file. This extension records the changes to be made on
top of that to produce the final index.</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>The signature for this extension is { 'l', 'i', 'n', 'k' }.</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>The extension consists of:</code></pre>
</div></div>
<div class="ulist"><ul>
<li>
<p>
160-bit SHA-1 of the shared index file. The shared index file path
    is $GIT_DIR/sharedindex.&lt;SHA-1&gt;. If all 160 bits are zero, the
    index does not require a shared index file.
</p>
</li>
<li>
<p>
An ewah-encoded delete bitmap, each bit represents an entry in the
    shared index. If a bit is set, its corresponding entry in the
    shared index will be removed from the final index.  Note, because
    a delete operation changes index entry positions, but we do need
    original positions in replace phase, it&#8217;s best to just mark
    entries for removal, then do a mass deletion after replacement.
</p>
</li>
<li>
<p>
An ewah-encoded replace bitmap, each bit represents an entry in
    the shared index. If a bit is set, its corresponding entry in the
    shared index will be replaced with an entry in this index
    file. All replaced entries are stored in sorted order in this
    index. The first "1" bit in the replace bitmap corresponds to the
    first index entry, the second "1" bit to the second entry and so
    on. Replaced entries may have empty path names to save space.
</p>
<div class="literalblock">
<div class="content">
<pre><code>The remaining index entries after replaced ones will be added to the
final index. These added entries are also sorted by entry name then
stage.</code></pre>
</div></div>
</li>
</ul></div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_untracked_cache">Untracked cache</h2>
<div class="sectionbody">
<div class="literalblock">
<div class="content">
<pre><code>Untracked cache saves the untracked file list and necessary data to
verify the cache. The signature for this extension is { 'U', 'N',
'T', 'R' }.</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>The extension starts with</code></pre>
</div></div>
<div class="ulist"><ul>
<li>
<p>
A sequence of NUL-terminated strings, preceded by the size of the
    sequence in variable width encoding. Each string describes the
    environment where the cache can be used.
</p>
</li>
<li>
<p>
Stat data of $GIT_DIR/info/exclude. See "Index entry" section from
    ctime field until "file size".
</p>
</li>
<li>
<p>
Stat data of core.excludesfile
</p>
</li>
<li>
<p>
32-bit dir_flags (see struct dir_struct)
</p>
</li>
<li>
<p>
160-bit SHA-1 of $GIT_DIR/info/exclude. Null SHA-1 means the file
    does not exist.
</p>
</li>
<li>
<p>
160-bit SHA-1 of core.excludesfile. Null SHA-1 means the file does
    not exist.
</p>
</li>
<li>
<p>
NUL-terminated string of per-dir exclude file name. This usually
    is ".gitignore".
</p>
</li>
<li>
<p>
The number of following directory blocks, variable width
    encoding. If this number is zero, the extension ends here with a
    following NUL.
</p>
</li>
<li>
<p>
A number of directory blocks in depth-first-search order, each
    consists of
</p>
</li>
<li>
<p>
The number of untracked entries, variable width encoding.
</p>
</li>
<li>
<p>
The number of sub-directory blocks, variable width encoding.
</p>
</li>
<li>
<p>
The directory name terminated by NUL.
</p>
</li>
<li>
<p>
A number of untrached file/dir names terminated by NUL.
</p>
</li>
</ul></div>
<div class="paragraph"><p>The remaining data of each directory block is grouped by type:</p></div>
<div class="ulist"><ul>
<li>
<p>
An ewah bitmap, the n-th bit marks whether the n-th directory has
    valid untracked cache entries.
</p>
</li>
<li>
<p>
An ewah bitmap, the n-th bit records "check-only" bit of
    read_directory_recursive() for the n-th directory.
</p>
</li>
<li>
<p>
An ewah bitmap, the n-th bit indicates whether SHA-1 and stat data
    is valid for the n-th directory and exists in the next data.
</p>
</li>
<li>
<p>
An array of stat data. The n-th data corresponds with the n-th
    "one" bit in the previous ewah bitmap.
</p>
</li>
<li>
<p>
An array of SHA-1. The n-th SHA-1 corresponds with the n-th "one" bit
    in the previous ewah bitmap.
</p>
</li>
<li>
<p>
One NUL.
</p>
</li>
</ul></div>
</div>
</div>
</div>
<div id="footnotes"><hr /></div>
<div id="footer">
<div id="footer-text">
Last updated 2015-05-26 14:38:11 PDT
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